An array of interrelated subprojects will be undertaken concurrently to investigate certain problems in the cytogenetics of differentiated chromosomes, for which the tomato is an ideal experimental medium. Intensive mapping of the tomato genome is planned, utilizing standard linkage tests and cytogenetic analysis. The improved understanding of the relationships between the cytological and genetic maps thus anticipated will expedite various investigations of interspecific hybrids and provide a broader basis for testing randomness in gene distribution (1) between chromosomes, (2) between arms of the same chromosome, (3) within arms, and (4) the distribution that seems peculiar to the nucleolar chromosome. The same survey will be compared with ones to be made from the latest summaries for other well investigated eukaryotes. Special emphasis will be paid to the distribution of loci for mimic genes as evidence of duplication of chromosomal segments within the tomato genome. Correlated experiments will be undertaken to synthesize new cytological deviants of potential usefulness for purposes of this program, including a 'segmental diploid', in which telosomes substitute for a single or homologous pair of normal chromosomes. The relative role of different arms and portions of arms in determining aneuploid phenotypes will be investigated by means of dosage studies in various kinds of trisomics and induced deficiencies. Studies on allozyme polymorphy will be continued to detect additional useful genetic loci and to provide independent tests of the relationships between wild and cultivated forms of the tomato species.